The present invention relates to a ballpoint pen tip, and also a ball point pen using the same. In detail, the invention relates to a ballpoint pen tip of such a type in which a ball receiving seat is formed by inwardly pressing and deforming a side wall in the vicinity of a front end portion of a metallic pipe body.
In the ballpoint pen tip of this type, conventionally, U.S. Pat. No. 5,899,625 and U.S. Pat. No. 5,904,432 disclosed a ballpoint pen tip in which a ratio (A/T) of an outer diameter A of a ball to a thickness T of a pipe is set to be 5.8 or less, and furthermore, a ratio (D/T) of a depth D of a concave portion to the thickness T of the pipe is set to be 2.0 or less in order to enhance a strength of a ball receiving seat, for example.
Although the conventional ballpoint pen tip having a comparatively small size (for example, 0.3 mm, 0.4 mm or 0.5 mm) is effective in enhancing the strength of the ball receiving seat, the ballpoint pen tip having a large size (for example, 1.0 mm or more) is not preferable in respect of manufacture because the quantity of projection (that is, the quantity of inward pressing and deformation) of an inwardly projecting portion for forming the ball receiving seat is more increased when the outer diameter of the ball is made greater so that a pressing force might be increased during the pressing and deformation and a front end portion of a tool such as a punch for the pressing and deformation might be damaged. On the other hand, even if the thickness of the pipe is simply set to be small in order to easily carry out the pressing and deformation, the thickness of the ball receiving seat itself is reduced so that the strength of the ball receiving seat is lowered.
In the ballpoint pen tip of this type (that is, a ballpoint pen tip of such a type as to form the ball receiving seat through the pressing and deformation), moreover, as the outer diameter of the ball is increased, the size of an ink flowing gap in a central portion of the ball receiving seat tends to be enlarged. Consequently, the capillary force of the ink flowing gap in the central portion is remarkably reduced as compared with that in the ink flowing gap between adjacent inwardly projecting portions. Therefore, it is impossible to rapidly supply ink to the whole ball having a large size so that a blur in handwriting or a break in handwriting might be caused.
In the conventional ballpoint pen tip, furthermore, a spew is easily generated on the outer peripheral edge of a rear end thereof. When the rear end of the ballpoint pen tip is to be pressed and fastened into a fitting hole formed in the front end portion of the penholder or the connecting member, consequently, the outer peripheral edge of the rear end of the ballpoint pen tip (a portion in which the spew is generated easily) bites at the inner face of the fitting hole so that the ballpoint pen tip might be hindered from being pressed and fitted smoothly or pressing and fitting failures might be caused, for example, the inner face of the fitting hole might be damaged. In particular, in the case of the ballpoint pen tip including a ball having a large size, it is necessary to apply a great pressing force depending on a large outer diameter of the pipe. In addition, when the biting at the outer peripheral edge of the rear end is caused, a much greater pressing force is required and the pressing and fitting operations are hard to carry out. Thus, there is a high possibility that the pressing and fitting failures might be caused.
In order to solve the conventional problems, it is an object of the invention to provide a ballpoint pen tip capable of obtaining a ball receiving seat having easiness of pressing and deformation, a sufficient ink fluidity, a smooth rotation of a ball and a sufficient strength and capable of being smoothly pressed and fitted in a fitting hole even if the ball having a large size is employed.
A ballpoint pen tip, according to the invention, rotatably holds a ball at its front end portion. The ball is held by a plurality of inwardly projecting portions for a ball receiving seat which is formed by inwardly pressing and deforming a neighborhood of a front end portion of a metallic pipe body 2 and a front end edge portion which is formed by inwardly pressing and deforming the front end portion of the pipe body. In the ballpoint pen tip according to the present invention, a relation of A/T greater than 5.8 is satisfied, where A is an outer diameter of the ball and T is a thickness of the pipe body.
The value of the ratio (A/T) of the outer diameter A of the ball to the thickness T of the pipe body 2 is greater than 5.8 (that is, xe2x80x9cA/T greater than 5.8xe2x80x9d). Therefore, even if the ball 5 having a large size is employed, pressing and deformation for forming the ball receiving seat can be carried out easily. The reason is as follows. Supposing that the value of A/T is equal to or smaller than 5.8 (that is, xe2x80x9cA/Txe2x89xa65.8xe2x80x9d), the thickness T of the pipe body 2 is comparatively increased and a great pressing force is required for forming the ball receiving seat even if a strength of the ball receiving seat can be enhanced. Consequently, there is a possibility that the front end portion of a tool (for example, a punch) for pressing and deformation might be damaged and it is hard to carry out manufacture through the pressing and deformation.
Furthermore, it is preferable that the value of A/T according to the present invention is made smaller than 10.0 (that is, xe2x80x9cA/T less than 10.0xe2x80x9d). Consequently, it is possible to obtain a ball receiving seat having a sufficient strength. The reason is as follows. If the value of A/T is equal to or greater than 10.0 (that is, xe2x80x9cA/Txe2x89xa710.0xe2x80x9d), the thickness T of the pipe body 2 to the outer diameter A of the ball is reduced too much so that the strength of the ball receiving seat is reduced remarkably. Consequently, there is a possibility that a smooth and stable rotation of the ball 5 cannot be obtained for a long period of time.
Accordingly, the ballpoint pen tip 1 according to the invention satisfies a relation of xe2x80x9c5.8 less than A/T less than 10.0xe2x80x9d. Consequently, even if the ball 5 having a large size is employed, it is possible to easily carry out the pressing and deformation for forming the ball receiving seat. In addition, it is possible to set such a proper thickness T that the strength of the ball receiving seat is not reduced.
In the ballpoint pen tip 1 according to the present invention, moreover, it is advantageous that a relation of xe2x80x9cD/T greater than 2.0xe2x80x9d should be satisfied, where D is a depth of a concave portion 32 which is formed at an outside of the inwardly projecting portions 3.
The value of the ratio (D/T) of the depth D of the concave portion 32 to the thickness T of the pipe body 2 is greater than 2.0 (that is, xe2x80x9cD/T greater than 2.0xe2x80x9d). Therefore, even if the ball 5 having a large size is employed, a sufficient ink fluidity can be obtained without causing a blur in handwriting or a break in handwriting. In addition, the ball 5 can be stabilized and supported sufficiently so that a smooth rotation of the ball 5 can be obtained.
The reason is as follows. If the value of D/T is equal to or smaller than 2.0 (that is, xe2x80x9cD/Txe2x89xa62.0xe2x80x9d), the depth D of the concave portion 32 to the thickness T of the pipe body 2 is reduced too much (that is, the quantity of projection of the inwardly projecting portion 3 is reduced too much). In particular, if the ball 5 has a large size, the capillary force of an ink discharging gap 31 in the central portion of the ball receiving seat becomes remarkably smaller than the capillary force of the ink discharging gap 31 (a radial groove) between the adjacent inwardly projecting portions 3. Consequently, the quantity of an ink to be supplied to the ball 5 is lacked so that a blur in handwriting or a break in handwriting is caused. Moreover, if xe2x80x9cD/Txe2x89xa62.0xe2x80x9d is obtained, the size of the ball receiving seat itself is reduced so that the ball 5 cannot be supported stably. Thus, there is a possibility that the smooth rotation of the ball 5 might not be obtained.
Furthermore, it is advantageous that the value of D/T according to the present invention should be set to be smaller than 4.0 (that is, xe2x80x9cD/T less than 4.0xe2x80x9d. Consequently, it is possible to easily carry out pressing and deformation, and furthermore, it is possible to obtain a ball receiving seat having a sufficient strength. The reason is as follows. If the value of D/T is equal to or greater than 4.0 (that is, xe2x80x9cD/Txe2x89xa74.0xe2x80x9d), the depth D of the concave portion 32 to the thickness T of the pipe body 2 (that is, the quantity of projection of the inwardly projecting portion 3) is increased too much so that the pressing force is increased during the formation of the concave portion 32. Therefore, there is a possibility that a front end portion of a tool such as a punch might be damaged. In this case, moreover, the thickness of the inwardly projecting portion 3 becomes remarkably smaller, through pressing and plastic deformation, than the thickness T of a portion of the pipe body 2 which is subjected to neither the pressing nor the plastic deformation. Therefore, there is a possibility that the strength of the ball receiving seat might be lacked.
Accordingly, the ballpoint pen tip 1 according to the invention satisfies a relation of xe2x80x9c2.0 less than D/T less than 4.0xe2x80x9d. Consequently, the thickness T of the pipe body 2 can be set more properly. Even if the ball 5 having a large size is employed, it is possible to avoid a blur in handwriting or a break in handwriting. In addition, it is possible to form a ball receiving seat through easy pressing and deformation without reducing the strength of the ball receiving seat.
The ballpoint pen tip 1 according to the invention mentioned above is more effective in the case in which a ball having a large size is employed. More specifically, it is preferable that the outer diameter A of the ball 5 should be set in the range of 0.7 mm to 1.6 mm . In particular, when the outer diameter A of the ball is set in the range of 0.7 mm to 1.6 mm (more preferably, in the range of 1.0 mm to 1.6 mm), functions and effects according to the invention mentioned above can be produced effectively. Consequently, it is possible to obtain a ball receiving seat having easiness of pressing and deformation, a sufficient ink fluidity, a smooth rotation of the ball and a sufficient strength.
In the ballpoint pen tip 1 according to the present invention, the inwardly projecting portions 3 may be provided in three places, preferably, four places or more.
When the inwardly projecting portions 3 are provided in four places or more, the ball receiving seat can be supported more stably than the case in which the inwardly projecting portion 3 is provided in three portions. Furthermore, in the case in which the number of ink discharging gaps 31 to be provided between the inwardly projecting portions 3 is not three but four or more, an ink can be caused to spread more rapidly over the whole surface of the ball 5 having a large surface area and a large size. Thus, it is possible to obtain a sufficient ink fluidity without causing a blur in handwriting or a break in handwriting. In particular, it is preferable that the number of inwardly projecting portions 3 should be four in that a sufficient ink fluidity can be satisfied and manufacture can be carried out easily.
In the ballpoint pen tip 1 according to the present invention, it is preferable that a curved surface portion 6 should be provided on an outer peripheral edge of a rear end of the pipe body 2.
Consequently, when the ballpoint pen tip 1 is to be pressed into a penholder and a fitting hole of a connecting member, the curved surface portion 6 and the inner face of the fitting hole slide smoothly and there is no possibility that the outer peripheral edge of the rear end of the pipe body 2 might bite at the inner face of the fitting hole to inhibit smooth pressing and fitting in the fitting hole or to generate pressing and fitting failures, for example, to damage the inner face of the fitting hole differently from the conventional art.
Examples of the shape of the pipe body 2 according to the invention include a right cylinder, a taper cylinder and a stepped cylinder having a small diameter portion and a large diameter portion.
The thickness T of the pipe body 2 according to the invention represents a thickness of a front end portion of the pipe body 2 in a part to which the pressing and deformation is not applied (that is, a thickness in the vicinity of the inwardly projecting portion 3) and does not represent thicknesses of the inwardly projecting portion 3 and the front end edge portion 4 which are reduced through the pressing and deformation. Moreover, the thickness T of the pipe body 2 can represent a mean thickness of the front end portion of the pipe body 2 in which the inwardly projecting portion 3 has not been formed.
The depth D of the concave portion 32 according to the invention represents a distance in a radial direction from an outer peripheral surface of the pipe body 2 of the concave portion 32 which has not been formed to the bottom most part of the concave portion 32 which has been formed (that is, the quantity of pressing and deformation in a radial direction of a side wall of the pipe body 2). Moreover, the concave portion 32 is provided in a plurality of places on the outer peripheral surface of the pipe body 2, and the depth D of the concave portion 32 is set to be equal. Furthermore, while the shape of the concave portion 32 may be any of a conical surface, a spherical surface and a prism, the shape of the conical surface is preferable in that the thickness can be changed uniformly and manufacture can be carried out easily.